Ammoxidation process

ABSTRACT

An ammoxidation process for the preparation of nitriles by reaction of an alkyl substituted aromatic hydrocarbon with ammonia and oxygen using as catalyst an α-alumina supported vanadium-alkali metal bronze promoted with boron, titanium, and tellurium whereby various desirable reaction parameters are obtainable. The invention also embodies the promoted catalyst.

Ammoxidation processes are well known in the art and numerous processeswith and without added oxygen and with numerous catalysts are describedin various U.S. and foreign patents and publications. In those processesusing added oxygen, several serious problems have hindered commercialdevelopment. One of the major problems where a nitrile is desired isthat the selectivity to nitrile products is low due to the burn ofhydrocarbon which reduces yield of nitrile products. It is alsonecessary for a commercially viable ammoxidation process to obtain goodconversion, a high yield of product, an efficient use of ammonia, and tooperate at relatively low mole ratios of ammonia and oxygen tohydrocarbon. A process that can achieve a plurality of theserequirements would represent a significant advance in the art.

The use of vanadium oxides as catalysts in ammoxidation processes iswell known. Also mixtures of vanadium oxide and other materials such asoxides of chromium, arsenic, selenium, sulfur, and antimony have beenused (see U.S. Pat. No. 3,544,617). Molybydenum oxide and heteropolyacids such as phosphomolybdic acid together with promotors of telluriumoxide are also known as ammoxidation catalysts (British Pat. No.948014). Tellurium and bismuth promoted cerium-molybdocyanadic acidshave also been disclosed as ammoxidation catalysts (U.S. Pat. No.3,452,077). British Pat. No. 957,022 discloses the use of solidphosphoric acid activated with numerous metals and non-metals, includingtitanium and boron, as catalysts for ammoxidation of propylene toacrylonitrile. Similarly, a mixture of vanadium pentoxide and telluriumoxide is suggested as an ammoxidation catalyst (Br. Pat. No. 1,133,216).More recently compounds known as vanadium bronzes have been disclosed ascatalysts for ammoxidation (see Belgian Pat. No. 820903) and niobium hasbeen used as a promotor for such catalysts, (U.S. Pat. No. 3,959,336).

It has now been found that an ammoxidation process which gives goodnitrile yields at high coversion and many of the other above mentionedobjectives is achieved by catalytically reacting an alkyl substitutedaromatic hydrocarbon with ammonia and oxygen using as catalyst avanadium-alkali metal bronze supported on α-alumina and promoted with aspecific combination of boron, titanium and tellurium. The inventionalso embodies the novel catalyst composition.

The process of the invention is carried out in either a fixed bed modeof operation or in a fluidized bed at a temperature between about 375°and 500° C., preferably 400° to 459° C., most preferably about 425° to435° C. The source of oxygen is preferably air, but any oxygen source issuitable. The amount of oxygen used in the process may vary over widelimits, but the process enables rather limited amounts of oxygen to beused and this, in turn, is favorable in that less burn of hydrocarbonreactant occurs. Thus, the ratio of oxygen to hydrocarbon in thereactant stream will usually be up to about 6:1, although it ispreferable to use no more than about 3:1, preferably 2.5:1 to 3:1,although about 2.0:1 is also quite useful. Likewise the ratio of ammoniato hydrocarbon used in the process of the invention will be preferablyabout 3:1, or less, most preferably 2.0:1 to 3:1 although higher ratios,up to 6:1 are also useful. It is also to be understood that the volumepercent concentration of reactants in the feed may be quite high ascompared to most ammoxidation procedures and the feed may comprise inpercent by volume 5 to 25% hydrocarbon, 6 to 20% oxygen, and 6 to 35%ammonia. In the preferred method, the volume percent concentration ofreactants corresponding to the above preferred ratios will comprise inpercent by volume from about 5 to about 7% p-xylene, from about 15 toabout 20% oxygen, and from about 10 to about 20% ammonia. The fact thatthe process of this invention makes possible this high concentration ofreactants is significant in contributing to a very efficient overallprocess.

As indicated, the hydrocarbon reactant will be an alkyl (preferablylower alkyl; e.g.; 1 to 4 carbon atoms such as methyl, ethyl, propyl andbutyl) substituted aromatic hydrocarbon and will be preferably of thebenzene and naphthalene series. Most preferably, a member of the benzeneseries will be used such as toluene and meta and-para-xylene. When usingm-xylene to obtain isophthalonitrile, however, it it preferred to employtemperatures at the lower end of the range given above and this is inaccord with art knowledge that m-xylene is more sensitive to carbonoxide formation than is the p-isomer.

It will be understood that the contact time for the reactants over thecatalyst will vary over a wide range, but will usually be from about 0.1to 20 seconds. The contact time actually used will depend upon catalystloading, catalyst volume, temperature and other parameters and theskilled art worker will have no difficulty in selecting an appropriatecontact time dependent upon these reaction parameters.

The reactant feed stream will, of course, contain other materials, asfor example, the inert ingredients of air, recycled intermediates (e.g.,a mononitrile when a dinitrile is desired) and possibly some smallamounts of other by-products associated with the recycle stream. Thisuse of a recycle stream will make possible a still more efficientprocess.

In addition to the above required parameters of the process it isessential that a particular type of material be used as catalyst. It isknown in the art that the addition of an alkali metal compound tovanadium pentoxide will, when the mixture is heated yield complexmaterials with anomalous valencies known as a vanadium bronzes. Suchlithium bronzes are discussed by Volkov et al., Zh. Neorg. Khim: 17 (6):1529-1532 (1972). Vanadium bronzes with sodium are described by Pouchardet al., Bull de la Soc. Chimique de France, No. 7, pages 2742-45 (1968),and No. 11 pages 4343-4348 (1967). Similarly, potassium containingvanadium bronzes are discussed by Holtzberg et al., J. Am. Chem. Soc.Vol. 78, pages 1536-40 (1956). Lithium bronzes are described by Hardy etal., Bull de la Soc. Chimique de France, No. 4, 1056-65 (1965) and byReisman et al., Jour Physical Chemistry 66 1181-85 (1962). Also ofinterest is the article by P. Hagenmuller entitled "Tungsten Bronzes,Comprehensive Inorganic Chemistry", edited by J. C. Bailar, Jr. et al.and published in 1973 by Pergamon Press.

All of the above references as well as the references which follow arehereby incorporated herein to teach the chemistry and preparation of thebronzes which are used in this invention.

These bronze materials are prepared by mixing an appropriate alkalimetal compound (e.g., carbonate, oxalate, etc.) with vanadium pentoxideand heating the mixture at an elevated temperature for several hours.Depending upon the amount of alkali metal ion added certain phases willbe established in accordance with the particular phase diagram pertinentto the mixture. Thus, for example, the Holtzberg et al article referredto above describes the potassium bronze system and the sodium system isshown in the article by Slobodin et al., J. Appl. Chem, (USSR) Vol. 38,pp. 799-803 (April 1965). Of the above alkali metal vanadium bronzes,all of which may be used in the process of the invention, the preferredbronzes for use as catalysts are the sodium bronzes and mixtures of thevarious species also may be employed. Preferred species include Bronze E(BZ I) which has an atomic ratio of sodium to vanadium of 0.167, BronzeII (BZ II) where the atomic ratio is 0.417, and an alpha prime phase(α'-phase) where the atomic ratio is 0.50. The terms Bronze I and BronzeII are used herein because these compounds correspond to the compoundscalled "first BRONZE" and "second BRONZE" by Slobovin and Fotiev, Jour.Applied Chemistry (USSR) 38 Vol. 4 pg. 799 April 1965 where the firstbronze is characterized by having 14.3 mole percent of Na₂ 0 in itscomposition (as does BZ I). These preferred Bronze I and α'-phasebronzes may be further characterized by the generic empirical formulaNa_(x) V₂ O₅ where x is greater than zero and equal to or less than 1.Other bronze systems of the Na_(x) V₂ O₅ species are known where x isgreater than 1 and these are useful in the process, but are somewhatunstable and therefore not preferred. The BZ I species may be consideredas Na₂ O.V₂ O₄. 5V.sub. 2 O₅ or Na₀.33 V₂ O₅ which is shown togetherwith related members of the series at pages 573 to 575 of Hagenmullerarticle as β-Na_(x) V₂ O₅ where x varies from 0.22 to 0.40, the βdesignation indicating the particular crystal phase structure of thecompound. The BZ II species may be considered as 5Na₂ O.V₂ O₄.11V₂ O₅ oras Na_(1+x) V₃ O₈ (x=0.25) which is isotypic with Li_(1=x) V₃ O₈ and isshown at page 584 of the Hagenmuller article mentioned above. Theα'-phase is characterized as Na_(x) V₂ O₅ where x+0.7 to 1.0 (see page577 of the Hagenmuller article). Also characteristic of the bronzes aretheir x-ray diffraction patterns wherein the strongest lines are asfollows:

BZ I: 9.6, 7.3, 4.75, 3.87, 3.47, 3.38, 3.21, 3.11, 3.08, 2.92, 2.90,2.727, 2.55, 2.45, 2.38, 2.18, 1.97, 1.87, 2.803, 1.74, 1.535, 1.492.

BZ II: 6.9, 7.04, 5.81, 3.87, 3.62, 3.50, 3.45, 3.21, 3.10, 3.01, 3.67,2.57, 2.43, 2.32, 2.27, 2.02, 1.97, 1.96, 1.81, 1.72, 1.86, 1.504,1.333, 1.39.

α': 11.3, 5.645, 4.82, 4.436, 3.667, 3.456, 2.967, 2.889, 2.882, 2.799,2.604, 2.436, 2.412, 2.291, 2.0196, 1.889, 1.803, 1.77, 1.689, 1.635,1.592, 1.479.

The α-prime phase as with the other bronzes may be obtained by themethods described in the literature and placed on the support for use inthe process, or it may be made in situ. This is readily achieved bytreating the BZ II on the support with a reducing atmosphere (e.g.,ammonia) or a stream similar to the hydrocarbon, ammonia and oxygen;e.g., an oxygen to hydrocarbon mole ratio of less than about 3.0.

As indicated the catalyst bronzes may comprise a mixture of the abovediscussed bronzes and preferred catalysts will comprise a mixturepredominant in either BZ II or the α-prime phase or both. While BZ Iused above is operable, it is preferred in order to keep the carbonoxides to a minimum to avoid having a predominant amount of BZ I in thecatalyst composition.

In order to obtain the specific promoted catalyst used in the invention,the appropriate compounds are simply added during the catalystpreparation. In one technique the oxides of boron (e.g. B₂ O₃), titanium(e.g. TiO₂) and tellurium (e.g. TeO₂) are added to all of the powderedcatalyst ingredients (including the support) and physically mixed andthe mixture pressed into pellets for use. In another technique, watersoluble salts (e.g., sodium borate, titanium oxalate, and sodiumtellurite) are added and used with the other catalyst ingredients toimpregnate the support. The amount of total promotor loading on thetotal catalyst and its support will be from about 4.1 to about 6.3% byweight calculated as the promotor oxides on the total finished catalyst(e.g. catalyst, promotors and support). However, the proportion of boronis very important since experimental data has shown that in order toachieve the advantages of the process the amount of boron promotor mustbe from about 0.15 to about 0.3 weight percent (as oxide) of the totalcatalyst and its support. The amount of titanium and tellurium will beon the order of about 2 to about 3% by weight (as oxides) of the totalcatalyst and support and although more may be used it is not usuallyeconomic to do so.

The catalyst support used in the process of the invention will becomprised of α-alumina. α-alumina is well known in the art and isexemplified by natural corundum and by the synthetic varieties which arecommercially available. These materials have a high density (on theorder of about 0.75 to 1.0 gm/cc.) and very low surface area (on theorder of 6m² /gm or less). Generally the α-alumina will contain enoughsodium ions so that the sodium bronzes may be made without any additionof sodium or other alkali metal compounds, but if insufficient sodium ispresent, enough may be added to give the desired bronze. In making thesupported catalyst all that is required is to make an aqueous slurry ofpowdered (170 mesh or finer α-alumina, alkali metal salt (preferablycarbonate) V₂ O₅ and promotor compounds, evaporate off the water,pelletize and calcine the pellets at about 500°-600° C. for severalhours, while passing a slow flow of air through the furnace.Alternatively the catalyst may be placed on the support by animpregnation technique where an aqueous vanadium oxalate solutioncontaining the appropriate amount of alkali metal and promotor compundsare deposited onto the α-alumina support.

As pointed out above, in making the catalyst alkali metal ions (usuallyin the form of the carbonate) are added to ensure that a bronze isformed. In a particularly preferred catalyst system where asodium-vanadium bronze is desired, the amount of sodium ion employed tomake the catalyst will be at a ratio of sodium to vanadium of 0.30 andsuch catalyst appears to be of high bronze purity devoid of extraneousmaterials which might degrade catalyst performance.

The amount of catalyst on the support (e.g., catalyst loading) will befrom about 1 to 20% by weight, preferably about 3 to 8%. The surfacearea of the catalysts used in the process is generally quite low beingless than 10m² /gm and usually 1 to 5m² /gm.

After the promoted BZ I or a promoted mixed BZ I and BZ II catalyst isprepared, but before its use, it is preferred to age the catalyst by aheat treatment at about 500° to about 750° C. for 3 to 4 hours. Thistreatment will convert most, if not all, of the BZ I to BZ II which ispreferred over BZ I.

The catalyst composition of the invention is thus a supported alkalimetal vanadium bronze promoted with from about 0.15 to about 0.3% byweight of B₂ O₃, on the order of about 2% to about 3% of TiO₂ and about2 to about 3% of TeO₂ and is preferably a promoted Bronze II or α-primephase catalyst. The support for the catalyst, as pointed out above, isα- alumina and the supported catalyst is preferably pelletized for use,but may also be employed in powder form.

The ammoxidation is carried out preferably in conventional fixed orfluidized bed apparatus, the reaction gases passing over the catalyst atreaction temperature and the effluent gases separated into theappropriate product and recycle streams. Particular advantages of theprocess of the invention reside in (a) low formation of carbon oxides,(b) high selectivity for formation of nitriles, (c) low oxygen andammonia to hydrocarbon ratios, (e) efficient use of ammonia, (e) reduceddealkylation of polyalkyl aromatics and (f) rather low processtemperature. In order to further describe and illustrate the inventionthe following examples are given:

PREPARATION OF CATALYSTS Method A

The α-alumina support is ground into a fine powder having a particlesize of about 170 mesh or less and the appropriate amount of B₂ O₃,TiO₂, TeO₂ and V₂ O₅ added to it. If analysis shows that the amount ofalkali metal in the α-alumina is insufficient the desired amount sodiumcarbonate or other alkali metal salt is added. The mixture is ground dryand then water is added and the mixture further agitated to make aslurry. The slurry is poured into an evaporating dish and evaporated todryness. The dry residue is mixed further to break up agglomerates andwater added to make a paste which is formed into pellets and thencalcined at 540° C. for about 4 hours while air at the rate of 2.5 l/minis passed through the furnace. After cooling the catalyst pellets areready for use.

Method B

Granulated alumina (8-16 mesh) is heated at 1300° C. for 4 hours. Watersoluble salts of the promoters and vanadium pentoxide are suspended in 5parts of water, heated to 80° C., and oxalic acid is added slowly toobtain a blue-colored vanadium oxalate solution. Sodium carbonate, asneeded, is added and the alumina is also placed in the solution. Themixture is dried over a water bath with agitation. While air is pumpedin, it is indurated in a furnace at 400° C. for 16 hours to obtain thecatalyst which is ready for use after cooling.

EXPERIMENTAL PROCEDURES

An appropriate quantity of catalyst (with or without inert diluent,e.g., quartz) was placed in a fixed bed 1/4 inch annular stainless steelreactor. Inert packing above the catalyst serves as a preheater sectionand a small amount (about 1-2 inches) of similar inert packing wasplaced in the bottom of the reactor to support the catalyst in thereaction zone. The upper end of the reactor was equipped with anassembly having multiple openings through which the hydrocarbons,ammonia, and air (or oxygen-helium or oxygen-nitrogen mixtures) can bemetered. The reactants were fed into the reactor which was operated at30 psig. The rate of gas flow was adjusted so as to produce the desiredcontact time at a given reaction temperature and pressure over a givenvolume of catalyst.

The effluent gases were passed from the reactor into a chilled flaskwhere the products were collected along with ammonium carbonate andwater. The remaining escaping gas was passed through a cold water cooledcondenser, a water trap, an acid trap, a wet test meter, and finallycaptured in a large polyvinylchloride bag. The reaction products wereextracted with acetonitrile and water, the solid products filtered offand the filtrate separated into solvent and water layers.

The analysis of the organic layer, water layer, gas sample from the bag,and the water trap, the acid trap, and the volume of the wet test meterenables calculation of the results (i.e., conversion, carbon balance,yield, etc.).

Examples I-IV

Using the above described procedure catalysts of a sodium-vanadiumbronze on α-alumina containing 8% vanadium (as V₂ O₅) and variousamounts of promotors was prepared. Operating data for the ammoxidationprocess and the results obtained are shown in Table I.

                                      TABLE I                                     __________________________________________________________________________    Ammoxidation of p-Xylene To Nitriles                                          __________________________________________________________________________    Catalyst: Sodium-Vanadium Bronze (8% by wt.) on α-alumina               promoted with boron, titanium, and tellurium.                                 __________________________________________________________________________                      Yield (Mole Percent)                                        Wt. %  Temp.                        Ratio     %                               B/Ti/Te                                                                              Range % Con-                                                                             Carbon       Total                                                                              TPN  % NH.sub.3                                                                         Plant                           (As oxides)                                                                          ° C                                                                          version                                                                            oxides                                                                             TN* TPN.sup.+                                                                         Nitriles                                                                           Nitriles                                                                           Burn Yield                           __________________________________________________________________________    I Mole Ratio- NH.sub.3 :p-xylene=2.5; O.sub.2 :p-xylene=2.5                                                       Contact Time=4.8 sec.                     a)  2/2/2                                                                            401/406                                                                              2.5 12.7  80.0                                                                             3.8 83.8 0.045                                                                              27.2 70                              b) .5/2/2                                                                            410/416                                                                              7.1 4.9  84.6                                                                               9.4                                                                              94.0 0.100                                                                              20.9 89                              c) .2/2/2                                                                            400/445                                                                             42.4 5.1  63.9                                                                              30.9                                                                              94.8 0.326                                                                              18.6 91                              d) .1/2/2                                                                            400/436                                                                             37.5 5.8  62.8                                                                              31.1                                                                              93.9 0.331                                                                               8.0 90                              e) .2/0/2                                                                            410/426                                                                             20.2 5.1  78.6                                                                              15.8                                                                              94.4 0.168                                                                              16.0 90                              f) .2/2/0                                                                            401/450                                                                             35.6 7.2  59.1                                                                              33.3                                                                              92.4 0.360                                                                              14.4 87                              II Mole Ratio- NH.sub.3 :p-xylene=5; O.sub.2 :p-xylene=4                                                          Contact time=7 sec.                       a)  2/2/2                                                                            420/430                                                                              9.0 11.5 72.6                                                                              13.8                                                                              86.4 0.160                                                                              34.4 76.5                            b) .5/2/2                                                                            420/425                                                                             15.5 6.3  78.4                                                                              14.6                                                                              93.0 0.157                                                                              32.9 87.6                            c) .2/2/2                                                                            400/426                                                                             60.9 8.1  42.2                                                                              49.1                                                                              91.3 0.538                                                                              19.9 87.8                            d) .1/2/2                                                                            420/441                                                                             48.0 6.0  54.5                                                                              39.0                                                                              93.5 0.418                                                                              37.2 90.5                            e) .2/0/2                                                                            420/442                                                                             35.8 5.9  69.6                                                                              24.2                                                                              93.8 0.258                                                                              30.8 89.5                            f) .2/2/0                                                                            419/440                                                                             34.9 8.7  69.1                                                                              21.9                                                                              91.0 0.241                                                                              27.6 84.8                            III Mole Ratio- NH.sub.3 :p-xylene=3; O.sub.2 :p-xylene=2.5                                                       Contact Time=14.5 sec.                    a)  2/2/2                                                                            420/426                                                                             14.1 10.7 73.4                                                                              12.9                                                                              86.3 0.150                                                                              57.7 76.3                            b) .5/2/2                                                                            420/427                                                                             24.6 6.2  73.7                                                                              18.9                                                                              92.6 0.204                                                                              26.4 87.0                            c) .2/2/2                                                                            418/435                                                                             56.1 5.7  56.0                                                                              37.8                                                                              93.8 0.403                                                                              18.2 90.4                            d) .1/2/2                                                                            420/432                                                                             46.0 8.2  50.8                                                                              40.2                                                                              91.0 0.442                                                                              28.0 86.3                            e) .2/0/2                                                                            420/435                                                                             46.0 6.4  61.2                                                                              31.5                                                                              92.7 0.340                                                                              29.9 88.2                            f) .2/2/0                                                                            420/441                                                                             52.2 9.2  53.6                                                                              36.4                                                                              90.0 0.405                                                                              22.2 84.7                            IV Mole Ratio- NH.sub.3  :p-xylene=3.0; O.sub.2 :p-xylene=2.5                                                     Contact Time=9 sec.                       a)  2/2/2                                                                            421/421                                                                              7.1 9.2  76.8                                                                              12.0                                                                              88.8 0.135                                                                              20.0 80.3                            b) .5/2/2                                                                            420/428                                                                             15.2 5.5  77.4                                                                              15.8                                                                              93.2 0.170                                                                              26.5 88.1                            c) .2/2/2                                                                            420/451                                                                             54.4 6.0  57.1                                                                              36.2                                                                              93.3 0.388                                                                              21.5 9.6                             d) .1/2/2                                                                            420/450                                                                             45.0 10.1 47.3                                                                              41.6                                                                              88.9 0.468                                                                              27.8 83.7                            e) .2/2/0                                                                            420/449                                                                             46.0 7.6  52.1                                                                              39.8                                                                              91.9 0.433                                                                              20.5 87.6                            __________________________________________________________________________      *TN=Tolunitrile                                                              .sup.+ TPN=Terephthonitrile                                              

As can be seen from the above Table I a plurality of desirable reactionparameters are achieved in runs Ic, IIc, IIIc and IVc, where the processis operated under the defined conditions of the invention. It is to beunderstood that in the operation of high volume commercial processessuch as the ammoxidation process of this invention, a cost benefitanalysis determines the optimum parameters for use. Even smallimprovements become significant because of the large volumes involved.Thus, a trade-off of the various parameters must be made and even thoughone or more particular parameters may be less than optimum, the overallprocess is the most efficient from an economic standpoint. In the abovedata in the C-case with a plurality of favorable parameters representsthe most economical process within its set.

Example V

In a similar ammoxidation with M-xylene at 436° C. using the catalyst ofIc the process gave a 37.6% conversion, carbon oxides formation in theamount of 15.49 mole %, total nitriles in the amount of 83 mole %, anammonia burn of 6.2% and a plant yield of 77%.

The invention claimed is:
 1. In the ammoxidation process of a loweralkyl substituted aromatic hydrocarbon to the corresponding nitriles,which process is carried out by reacting said hydrocarbon with ammoniaand oxygen at about 375° to about 500° C., the improvement of using ascatalyst an alkali metal vanadium bronze supported on α-alumina andpromoted with about 2 to about 3% of tellurium, about 2 to about 3% oftitanium and about 0.15% to about 0.3% of boron, said percentages beingby weight of the total catalyst and its support.
 2. An ammoxidationprocess for preparing nitriles from m- and p-xylene which comprisesreacting said xylene and ammonia at a temperature of from about 375° toabout 500° C. in the presence of added oxygen, the molar ratio ofammonia to xylene being from about 2.0:1 to about 6:1, the volumepercent concentration of the reactant feed being about 5 to 25% xylene,6 to 35% ammonia, and 6 to 20% oxygen, and the catalyst for saidreaction comprising at least about 1 to 20% by weight of an alkali metalvanadium bronze supported on α -alumina and promoted with about 2 toabout 3% of tellurium, about 2 to about 3% of titanium and about 0.15 toabout 0.3% of boron, said percentages being by weight of the totalcatalyst and its support.
 3. An ammoxidation process for preparingterephthalonitrile from p-xylene which comprises reacting p-xylene andammonia at a temperature of from about 400° to about 450° C. in thepresence of added oxygen, the molar ratio of oxygen to xylene being fromabout 2:1 to about 3:1, the volume percent concentration of the reactantfeed being about 5 to 25% xylene, 6 to 35% ammonia, and 6 to 20% oxygen,and the catalyst for said reaction comprising at least about 1 to 10% byweight of an alkali metal vanadium bronze supported on α-alumina andpromoted with about 2 to about 3% of tellurium, about 2 to about 3% oftitanium and about 0.15 to about 0.3% of boron, said percentages beingby weight of the total catalyst and its support.
 4. The process of claim3 where the catalyst is a sodium vanadium bronze.
 5. The process ofclaim 4 where the catalyst is predominantly BZ II or the α-prime phase.6. The process of claim 3 operated in a fixed bed mode at essentiallyatmospheric pressure where the temperature is from about 400° to about435° C, the ratio of oxygen to xylene and of ammonia to xylene is fromabout 2.0:1 to about 3.0:1, and the concentration of feed by volume isabout 5 to about 7% xylene, about 10 to about 20% ammonia and about 15to about 20% oxygen, and the catalyst is a sodium vanadium bronze. 7.The process of claim 6 where the catalyst is predominantly BZ II.
 8. Theprocess of claim 6 where the catalyst is predominantly the α -primephase.
 9. The process of claim 6 where the catalyst is a mixture of BZII and the α -prime phase.
 10. The process of claim 3 operated in afluidized bed mode at 1 to about 5 atmospheres where the temperature isfrom about 400° to about 435° C, the ratio of oxygen to xylene and ofammonia to xylene is from about 2.0:1 to about 3.0:1, the concentrationof feed by volume is about 5 to about 7% xylene about 10% to about 20%ammonia and about 15% to about 20% oxygen, and the catalyst is a sodiumvanadium bronze.
 11. The process of claim 10 where the catalyst ispredominantly BZ II.
 12. The process of claim 11 where the catalyst ispredominantly the α-prime phase.
 13. The process of claim 11 where thecatalyst is a mixture of BZ II and the α-prime phase.
 14. The process ofclaim 6 where the xylene is m-xylene and the reaction temperature isfrom about 375° to about 425° C.
 15. The process of claim 2 operated ina fixed bed where the xylene is meta-zylene and the reaction temperatureis from about 375° to about 500° C.
 16. The process of claim 2 operatedin a fluidized bed where the xylene is m-xylene and the reactiontemperature is from about 375° to about 500° C.